Two-way telephone system



April 30, 1995. E. R. TAYLOR ET A1.

TWO-WAY TELEPHONE SYSTEM Filed June 16, 1931 v KMX wam h.

ATTORNEY UNETE STATES PATE 1,999,346 TWO -WAY TELEPHONE SYSTEM Edmund R.riaylor, New York, N. Y., and Doren Mitchell, Martinsville, N. J.,assignors to American Telephone and Telegraph Company, a corporation oi"New York Application June 16, 1931, Serial No. 544,891 10 Claims. (Cl.179-170) This invention relates to systems for the transnormallydisabled channel at the receiving end mission of energy between distantstations for the of the system. production of some desired over-alleffect. More The applicants transmission C0nt101 apparaparticularly, theinvention relates to two-way teletus is preferably COllned t0 theterminal Sta- 5 phone systems having wave-responsive devices for tions,as distinguished from the intermediate Centrelling transmission, such assinging supradio stations, and is of such a nature that, should pressorsand echo suppressors. c it be desirable to shift the operation of thesystem In a long telephone system it is often desirable, from the use ofcontrol currents to the control of in Order to prevent singing, to haveone or both transmission by voice waves without special curio of theoneway paths normally disabled at one Tents, Only miner and readily madealteratiOnS or more points. It follows that means must be Would berequired. provided whereby the voice waves will cause the These andother features and advantages of removal of any such disability normallyfoundon the aDDliCants methedsf and means fOr transthe path Other whichthesewaves are to be transmission control will be understood when thefoli; mitted. lowing detailed description of one desirable em- Thesystem, however, may include what will be bodiment of the invention isread with reference hereinafter termed a mutable 1ink-that is, a. to theaccompanying drawing, which shows dialink capable of or liable to change(from internal glamniateally, and in part schematically, the or externalcause) which may give rise to interalJplieatiOn t0 a 1011s tWO-Waytelephone system :o fering energy, or, more specifically, a linkspeincluding a radO linkoiauy subject to noise, fading (in the case ofradio With reference t0 the details 0f the drawing, transmission) orchange of impedance. In suon there is disclosed a two-Wav telephonesystem eX- a case, the wave-responsive devices on the receivtendingfrein Station W at the left t0 the distant ing side of the mutable link,when made suiii- Station E at the right- The system may be eX- cientlysensitive to operate on weak speech entended t0 the left from StatiOn WOVer the tWO- ergy, are liable to false operation by the interwirecircuit L, which is connected through the fer-ing energy originating inthe mutable link. usual hybrid COil and iS balanced by the llsllal Thisdifliculty is removed if control currents are network. Likewise, thesystem may be eXtended employed and the wavcyesp0nsive devices cn the tothe right from station E over the two-wire circuit L', which isconnected through a hybrid coil spend exclusively to the frequencies ofthe control and balanced by a network. The system extendcurients. Thesecontrol waves not only are easier ing betWeen StatiOIl W and StatiOIl Etakes the to detect, in spite of interfering noise waves, than form of afour-wire circuit. The intermediate the Speech Waves7 being Conned to a,narrow frcportion of this four-wire circuit consists of a radio :1,3quency band, but also have the advantage that link extending fromstation W at the left to statliey are applied suddenly with fullamplitude, tion E at the right. It will be understood that producing aprompt and positive operation of the station W may be at a greatdistance from stae transmission controlling relays. tion W and thatstation E' and E may be sep- The applicants invention is particularlyapalated by a great distance- 40 plicable to systems such as thatsuggested above. The Path adapted for transmission fmm left Moreparticularly, it is applicable to the shortt0 Tight comprises the OnewayWire Section LW wave radio-telephone systems used for transconnectingStations W and W" the radio link be Oceanie Communication tween thetransmitting antenna nt and -the ref: In general, the applicants applythe control ien/mg ajntenna.A2" and the-recenfmg WH? Sec" icu1rents`preferably, two or more control curnon LW extending fromstation E to staimn E' ,L 1 The path adapted for transmission from rightto lenYS of @mlent frequencles m each dlrectlonleft comprises theone-way wire section LE', the 12g itedpenods 1/Ihm n? V10 energy 1s bemgradio link between antennae A1' and A2, and the n m D e cause e commlequency`or any receiving wire section LE. It will be noted that 50 one.of, a ,plurality of @Html frequencies-t0 the left to right channel isnormally disabled at maintain disabled the recewing channel which is thepol-n1; 1, at Station W and at the point d at staadapted fortransmission from the mutable link. tion E. Likewise, the channel fortransmission and Cause the Voice Waves 011 the transmitting from rightto left is noi-many disabled at the point side of the mutable link todisconnect the sourceb at station E and at the point d at station W.

'l` GFFICE or sources-of control current and thus clear the Associatedwith the wire section LW at stationquencies which are generated andapplied to the path LW at station W. rlhe alternating-currents sogenerated and applied to the transmission paths are the controlcurrents.

Consideration being given particularly to transmission from station W tostation E, the frequencies f1 and f2 are normally sent over the path LWVto station W', are there applied to the radio transmitter and thetransmitting antenna A1, are picked up at the distant station E in theantenna Az', are applied to the radio receiver and are then sent overthe path LW to station E. There each control frequency passes throughthe appropriate filter and operates an amplifier-detector, fi operatingVamplifier-detector 3E' and f2 operating amplirier-detector 4B'. Relays3| and di are connected in the output circuits of amplifier-detectorsSil' and All', respectively. 1t will be understood that as long as thecontrol frequencies are transmitted these relays 3i and lli aremaintained in operated condition and that the operation of either one ofthese relays serves to disable the path LW at points d. While it is notof the essence of the invention, it is advantageous to use two or morecontrol currents of diirerent frequencies, which are usually outside thevoice range. Thus if selective fading eliminates one of the controlfrequencies in the radio link, it is likely that the other-or one of theothers, if more than two control frequencies are used-will betransmittedwith suincient strength to maintain one of the relays'operated to disable the transmission path at point'd. The generators offrequencies fi and f2 and the amplifier-detectors Bil and i areunderstood to represent any suitable number of generators andcorresponding ampli-- fier-detectors.

In the system specifically disclosed the transmission of controlcurrents from station E to station W is the same as the transmission inthe opposite direction.

At station W the amplifier-detector iii, controlling certain relays tobe discussed hereinbelow, is connected to the path LW atY point c and isresponsive to the voice waves. At the distant station E theamplifier-detector 2t is connected to the path LW at point c and, likeamplifier-detector iti, responds-to the voice waves. Likewise,amplifier-detectors Eil' at station E and 2E at station W respond tovoice waves traveling from right to left.

If voice waves from circuit L enter the transmission path LW, they passthrough a volume control device and a one-way amplifier to the point aat the input of a delay circuit. At this point a portion of the voiceenergy is diverted to operate amplifier-detector l. Relays il, i2 and i3are operated by this amplifier-detector. Relay serves to remove thedisability from the path LW at point b. The operation of relay i2disables balanced coil BCi and prevents the further application of thecontrol currents of frequencies f1 and f2. it should bev noted at thispoint that the filter in the output of the coil BCi is designedtoprevent theapplication to the transmission path of transients in thevoice range set up by the operation of the relay I2. The operation ofrelay I3 disables the balanced coil BCz in the opposite receiving pathLE, thus preventing transmission over that path. It should be noted thatif relay 2i has operated before the operation of amplifierdetector IEP,the relays i2 and i3 will not operate. This feature will be discussedhereinbelow.

The transmission of the voice waves beyond the point a in path LW isheld up slightly in the delay circuit, time thus being given for theclearing of the channel at point b by relay and the removal of thecontrol energy by the operation of relay i2.. The speech currents nowdivide in the hybrid coil, half of the energy being dissipated in thebalancing network and the other half being transmitted on to the radiotransmitter at station W'. At the distant end of the radio link thevoice waves are picked up in the radio receiver at station E and arethen sent on over path LW to station E. By the time the voice energyreaches station E the interruption of the control energy will havecaused the release of relays 3 I and 4 I and accordingly the disabilitywill have been removed from the path LW at the point d. Voice waves nowpass through the balanced coil BCz to the point c. At this point thewaves cause the operation of amplifier-detector 2li and relay 2|',unless relay i3' has operated, as will be discussed hereinbelow. theoutput circuit of amplifier-detector lil (associated with the oppositetransmitting path LE) and the circuits of relays Il', I2 and I3. Thisoperation secures control of the system at station E and preventsbreaking in by the subscriber connected to circuit L. Furthermore,echoes of the voice waves traveling Yfrom left to right, which may enterthe path-LE and operate the amplifierdetector Hi', are prevented frominterfering with the transmission over the path LW and from causingfalse operation of the relays i i and l2. Beyond point c' the voicewaves pass through the delay circuit, which has introduced the delaynecessary for the operation ofrelay 2|', the volume control device andthe one-way amplifier' to the circuit L'.

It should be noted in connection with transmission from station W tostation E that during the transmission of the voice waves relay |3 isheld operated. Accordingly, even if relays 3| and 4| should both releasemomentarily because of oontrol frequency fading in the radio link, thebalanced coil BC2 is held disabled and voice waves in the path LE cannotreach the point c to operate amplifier-detector 2i) and relay 2|. inother words, if the voice waves in path LW reach the point ci in time totake control of the left end of the system at station W through theoperation of relays Il and I3, later arriving energy in the oppositepath LE cannot interrupt this control. If, however, the voice energy inpath LE has reached point c without interruption, amplifierdetector 26and relay 2| will operate, and the control of the system at station W isgiven to the subscriber connected to station E.

The operation of the system in connection with transmission from righttoleft is, in the system specifically disclosed, in connection withtransmission from left to right. Control frequencies fi and f2 areapplied during the silent periods to the path LE', the filter attheoutput ofthe coil BCi passing the control frequencies but excluding thetransients in the voice range. These control frequencies reach thestation W and hold relays 3| and 4| (or one The operation of relay 2|breaks the same as that described of them, at least) operated to disablethe path LE at point d. When voice Waves travel over the circuit L andthe path LE', amplifier-detector l e' is operated. Relay ll removes thetransmission path disability at point 79'; relay l disables the coil B01and thus prevents the further application ci the control frequencies;and relay i3 disables the opposite transmission path LW at the coil B02.When the voice Waves reach the station W, the path LE has been renderedoperative by the release of relays 3l and di, and the voice waves travelon to the point c, unless relay i3 has operated in the meantime. Asdescribed above, the operation oi ainpliermdetector 2i) and relay 2isecures control by preventing interruption due o later arriving voiceWaves in the opposite path LW. The voice Waves in path LE are novv freeto pass on to the connected circuit L.

It remains to point out several advantages of the applicantsarrangements for transmission control:

The receiving path at either of the stations W and E is normally heldinoperative by the control currents; accordingly, noise energy comingfrom the radio link cannot pass over this receiving path to producefalse operation of the transmission control device the voice responsivecontrol devices be made very sensitive, so as to operate on the Wea-zestspeech.. This sensitivity of the voice responsive apparatus connected tothe receiving path serves to insure the prevention of false operation byecho currents returning over` the opposite transmitting path, as hasbeen described above. Accordingly, the receiving volume is practicallyindependent of noise originating in the mutable (radio) link.

It has been stated above that the control currents are usually offrequencies outside the voice range. Since these control currents aretransmitted from the radio transmitters only when no speech is beingtransmitted, no additional load capacity is required in thesetransmitters. As has been indicated above, the filters in 'the inputs ofampiiiier-dctectors Sil, til and fifi pass only the control frequenciesand thus prevent operation oi these ainplier-detectors by energy otherthan the control energy. it has been shown above that While a singlecontrol frequency may be employed in each direction oi transmission, itmay be preferable to use tvfo or more control freduencies, in order tofurnish some degree of insurance against damaging fading in the radiolink and the resultant undesirable transmission or" radio noise.

While the invention has been disclosed specifically in one desirableembodiment, it is -to be understood that the applicants methods of andapparatus for transmission control may take other and widely differentforms within the scope of the appended claims.

What is claimed is:

l. In a tivo-way systeni for the transmission of energy, two pathsadapted for transmission in opposite directions, means near thetransmitting terminal of one oi said paths for applying control energyto said path, means near the receiving terminal of said path responsivesubstantially only to said control energy for maintaining said path indisabied condition, means near the transmitting terminal of said pathresponsive to the energy transmitted thereover to produce the desiredover-all effect for preventing the application thereto of said controlenergy, and means near the transmitting terminal of said path responsiveto said energy transmitted to produce the desired overuall effect forcontrolling the transmission over both the transmission paths, near saidterminal, said last-mentioned means being independent of the applicationto the system or the Withdrawal therefrom of control energy designed topass over the receiving end oi the opposite path.

2. ln a tvvo-Way system for the transmission of energy, including aiii-st path adapted for transmission in one direction and a second pathadapted for transmission in the opposite direction, the method oftransmission control which consists in applying control energy to therst path near the transmitting end thereof, causing said control energyto maintain the rst path in disabied condition near the receiving endthereof, causing the energy transmitted for the production of thedesired over-ali eiiect, as it travels over the transmitting end ci thefirst path, to prevent the application of the control energy thereto,causing said energy transmitted for the production of the desiredover-all effect, as it travels over said transmitting end, to controlthe transmission over said iirst and second paths at that end of thesystem, and preventing the interruption of the last-nientioned controlby the application to the system or the Withdrawal therefrom of controlenergy designed to pass ovei said second path.

3. in a two-Way system for the transmission of energy, a iirst pathadapted for transmission in one direction, a second path adapted fortransmission in the opposite direction, means near the transmitting endof said first path for applying control energy thereto, means near thereceiving of said rst path responsive substantially only to said controlenergy for maintaining said path in disabled condition, means near thetransmitting end of said irst path responsive to the energy transmittedto produce the desired overall eiiect for preventing the application ofsaid control energy, means similarly responsive near the transmittingend of said rst path for controlling the transmission over said path andthe opposite sect-ion of said second path, and means near the receivingend of said second path and responsive to energy therein of earlierarrival than energy in the first path for rendering the paths exemptfrom control by energy in the iirst path, the control. ci thetransmitting end of said Erst path being independent of the applicationto the system the withdrawal thereirorn of control energy designed topass over said second path.

f-i. in a tivowv/ay signal transmission system, including two pathsadapted for transmission in opposite directions, the method oftransmission control which consists in applying control energy to eachpath when said path is not being used for signal transmission, causingthe control energy applied to a path to disable said path, causing thesignal energy applied to the transmitting end of apath to interrupt theapplication of the control energy thereto and to control thetransmission over the transmitting end thereof, and rendering a pathimmune to prevention or interruption of the signal control thereover bythe application to the system or the Withdrawal therefrom of controlenergy designed to pass Over the opposite path.

5. In a two-way transmission system, including two paths adapted fortransmission in opposite directions, the method of transmission controlwhich consists in applying control energy to each path when said path isnot being used for signal transmission, causing the control energyapplied to a path to disable said path near its receiving end, causingthe signal energy applied to the transmitting end of a path to interruptthe application of the control energy thereto and to control thetransmission over the transmitting end thereof and the receiving end ofthe opposite path, and rendering a path immune to prevention orinterruption of the signal control over the transmitting end thereof bythe application to the system or the withdrawal therefrom of controlenergy designed to pass over the opposite path.

5. ln a tivo-way system for the transmission of energy, including aiirst path adapted for transmission in one direction and a second pathadapted for transmission in the opposite direction, the method oftransmission control which consists in applying control energy to eachpath near the transmitting end thereof, causing said control energy tomaintain the path to whifh it is applied in disabled condition near thereceiving end thereof, causing the energy transmitted for the productionof the desired over-all efrect, as it travels over the transmitting endof one of said paths, to prevent the application or" the control energythereto, causing said energy transmitted for the production or" thedesired over-all eect, it travels over said transmitting end, to controlthe transmission over said first and second paths at that end of thesystem, and rendering the transmission over said transmitting end of thepath immune to interruption by the application to the system or thewithdrawal therefrom oi control energy designed to pass over said secondpath,

7. ln a two-Way signal transmission system, including two paths adaptedfor transmission in opposite directions, means associated With each pathfor applying control energy thereto when such path is not being used forsignal transmission, means associated with each path and responsive tosaid control energy for maintaining the path inoperative for signaltransmission, means responsive to the application of signal energy toeither path for interrupting the application of control energy thereto,and means associated with the transmitting end of one of said paths andresponsive to signal energy therein for controlling the transmissionthereover, said last mentioned means being independent of theapplication to the system or the Withdrawal therefrom of control energydesigned to pass over the opposite path.

8. In a two-Way signal transmission system, including two paths adaptedfor transmission in opposite directions, means associated with each pathi for applying control energy thereto when such path is not being usedfor signal transmission, means associated with the receiving end o eachpath and responsive to said control energyv for maintaining the pathinoperative for signal transmission, meansresponsive to the applicationof' signal energy to either path for interrupting the application ofcontrol energy thereto and means associated With the transmitting end ofone of said paths and responsive to signal energy therein forcontrolling the transmission thereover and over the receiving end of theopposite path, said last mentioned means being independent of theapplication to the system or the withdrawal therefrom of control energydesigned to pass over the opposite path.

9. In a two-Way signal transmission system, including two paths adaptedfor transmission in opposite directions, means associated with each pathfor applying control energy thereto when such path is not being used forsignal transmission, means associated with each of said control energyapplying means for preventing the application of transients in thesignal frequency range to the transmission path as a result of theoperation of said control energy applying means, means associated witheach path and responsive to said control energy for maintaining thepathinoperative for signal transmission, means responsive to the applicationof signal energy to either path for interrupting the application ofcontrol energy thereto, and means associated with the transmitting endof one or said paths and responsive to signal energy therein forcontrolling the transmission thereover, said last-mentioned means beingindependent of the application to the system or the Withdrawal tLereirorn of control energy designed to pass over the opposite path.

lo. In a two-Way signal transmission system, including two paths adaptedfor transmission in opposite directions, means associated with each pathfor applying control energy thereto when such path is not being used forsignal transmission, means associated with each of said control energyapplying means for preventing the application of transients in thesignal frequency range to the transmission path as a result of theoperation of said control energy applying means, means associated Withthe receiving end' of each path and responsive to said control energyfor maintaining the path inoperative for signal transmission, meansresponsive to the application of signal energy to either path forinterrupting the application of control energy thereto, and meansassociated with the transmitting end of one of said paths and responsiveto signal energy therein for controlling the transmission thereover andover the receiving end of the opposite path, said last-mentioned meansbeing independent of the application t the system or the Withdrawaltherefrom of control energy designed to pass over said opposite path.

EDMUND R. TAYLOR. DOREN MITCHELL.

